Hot air generator



Dec. 2, 1969 c, REICHELDERFER 3,481,321

HOT AIR GENERATOR Filed April 11, 1968 5 Sheets-Sheet J.

INVENTOR CHArzLes Afiemusw'sawsra.

ATTORNEYS Dec. 2, 1969 c. A. REICYHELDERFER HOT AIR GENERATOR 3 Sheets-Sheet 2 Filed April 11, 1968 INVENTOR CHAraLEs A.l?elcue LDEIZFEP.

BY muse-5 1M "i 8mm ATTORNEYS United States Patent US. Cl. 126-99 8 Claims ABSTRACT OF THE DISCLOSURE An air heating unit for heating air to be supplied to a space to be conditioned, the unit having a heat exchanger formed of like corrugated side walls and flue elements having corrugated sheet walls, wherein the corrugations are inclined slightly to a selected axis of the heat exchanger and the corrugations of oposite walls are inclined in opposite directions.

Background and objects of the invention In warm air furnaces, the heat exchanger structure which isolates the products of combustion of fuel from the air to be heated and transfers heat to the air to be heated is usually of such construction that it has a large thermal mass. Because of this large thermal mass, and the time required to bring the surfaces of the heat exchanger exposed to the air up to the desired range of temperatures, special controls are usually required to delay the flow of air for a time following initiation of combustion of the fuel tolimit the flow of uncomfortably cold air. Also, prior art heat exchangers for warm air furnaces, as customarily made, are frequently limited in regard to the orientation of the furnace, and are thus unsuitable for installation conditions which may require the furnace to be oriented, for example, in horizontal direction when the structure is designed for a vertical flow of the air being heated. Further, conventional heat exchanger designs are subject to problems of stresses resulting from unequal expansion and high temperature gradients, and to the weight of materials normally employed in the construction of such heat exchangers.

An object of the present invention is the provision of an extremely compact heat exchanger suitable for use with comfort space conditioning systems, particularly for residences, apartments and small commercial buildings, providing a highly eflicient, high pressure hot air generator for use with small duct systems, for example the type described in the copending patent application Ser. No. 690,253, entitled Heating and Cooling System, filed in the name of John J. Dieckmann.

Another object of the present invention is the provision of a heat exchanger for hot air generators which will extract a maximum amount of heat from products of combustion of fuel and transfer the heat to a minimum amount of air being heated, in such manner that the final temperature of the air is substantially higher than the usual temperature of the air leaving space heating furnaces of conventional designs.

Another object of the present invention is the provision of a novel heat exchanger structure for hot air generators, having relatively small mass in proportion to its heat transfer capacity to provide rapid response to changes in heat input rate and permit elimination of need for special starting controls.

Another object of the present invention is the provision of a novel hot air generator having a heat exchanger constructed in such manner that the hot air generator is free from orientation limitation, so that it will perform equally as well in installations requiring upward flow, downward flow or horizontal flow of the air to be heated.

Another object of the present invention is the provi- 3,481,321 Patented Dec. 2, 1969 FIGURE 1 is a perspective view of a hot air generator embodying the present invention, with parts of the outer shell broken away to illustrate the internal construction thereof;

FIGURE 2 is a perspective view of the heat exchanger embodying the present invention;

FIGURE 3 is a horizontal transverse section view of the hot air generator and the heat exchanger section thereof taken along the line 33 of FIGURE 1;

FIGURE 4 is a fragmentary perspective view of an assembly of flue elements forming a portion of the heat exchanger;

FIGURE 5 is a side elevation view of an assembly of one pair of the corrugated shells forming one flue element, with a portion of one of the Walls broken away to reveal the other wall, and

FIGURE 6 is a horizontal section view through one assembled pair of the corrugated shells forming one flue element, taken along line 6-6 of FIGURE 5.

Detailed description of a preferred embodiment of the invention While the hot air generator of the present invention is suitable for operation with any direction of air flow, upward, downward or horizontal, for purposes of convenience of illustration and to describe its operation in the most simple manner, the following description is directed to an embodiment wherein the air flow is vertically upward.

Referring to the drawings, wherein like reference characters designate corresponding parts throughout the several figures, the hot air generator, generally indicated by the reference character 10, employs an essentially airtight jacket or outer wrapper 11 enclosing three sides of the generator 10, having side panels 12 and 13, rear panel 14, top panel 15 and bottom panel 16. The front or fourth side of the enclosure is covered by a readily dismountable access panel 17. A blower 18 driven by a motor 19 is mounted in the lower compartment of the jacket 11, defined by the intermediate horizontal partition 20, and draws return air through an inlet connection (not shown) and discharges the same into the heating zone 21 above the partition 20 through the outlet opening 22 provided in this partition and forming the discharge opening of the scroll of the blower 18. V

In the embodiment herein illustrated, the heat exchanger 25 is a hollow sheet metal structure of essentially cubical configuration, formed of three identical vertical sides 26, 27 and 28, top and bottom sides 29 and 30, and a front side 31 having a burner inlet 32 and an exhaust outlet 33. The bottom side 30 of the heat exchanger 25 is spaced somewhat above the upper surface of the horizontal partition 20, providing a space for free flow'below the heat exchanger of the air discharged from the blower 18. A generally vertical mounting plate 34 is attached to the heat exchanger front wall 31 through a gas-tight flange joint in covering relation to the burner inlet 32 and extending downwardly to the horizontal partition 20. This mounting plate 34 supports an air inlet plenum 35 in the lower region thereof, communicating with the space between the heat exchanger bottom wall 30 in the partition through a port 36. Immediately above the air inlet plenum 35 and also mounted on the mounting plate 34 is a burner 37 which receives fuel through a fuel supply conduit 38. Thus, in this preferred embodiment, the blower 18 supplies the combustion air for the burner by discharging combustion air through the port 36 into the air inlet plenum 35 and then to the burner 37. It will be understood, of course, that combustion air may be supplied to the burner 37 by other means, such as a second blower supplying air directly to the burner plenum 35.

In the event it is desired that the hot air generator 10 also serve as a source of cooled air for the space conditioning system, a heat exchange coil (not shown) of known design may be located in the space below the blower 18 for the purpose of cooling the entering air. This cooling coil may be connected in conventional manner by supply and return pipes to a remote refrigeration apparatus and conventional control devices may be provided to permit selective alternate operation of either the refrigeration apparatus or the burner 37, as desired, to either cool or heat the air being supplied from the generator 10.

The heat exchanger 25, as is more clearly illustrated in FIGURES 2, 3, 4 and 5, is generally cubical structure wherein the three identical sides 26, 27 and 28, the top and bottom walls 29, 30 and the front walls 31 are all welded into a single gas-tight structure permitting the products of combustion and air being heated to pass in heat exchange relation While maintaining the same physically separated from each other. The identical vertical sides 26, 27 and 28 are formed of corrugated steel stampings having sinuous corrugations 39 extending from the top to the bottom horizontal edges, while the portions immediately adjacent the vertical edges are left in uncorrugated condition.

The heat exchanger is divided into a substantially U-shaped chamber, when viewed in top plan view, as seen in FIGURE 3, by a first flue element 40 extending substantially along the fore and aft center line of the heat exchanger from the front wall 31 thereof over a major portion of the distance to the rear wall 27, forming an internal, substantially centrally disposed divider separating the interior of the heat exchanger 25 into an upstream leg 41, forming substantially the right hand half of the heat exchanger as viewed in FIGURE 3, and a downstream leg 42, forming substantially the left hand half of the heat exchanger. The legs 41 and 42 are in open communication with each other through the portion 43 of the heat exchanger adjacent the rear wall 27 thereof between the latter and the rearmost extent of the flue element 40. An array of similar flue elements 44 arranged in parallel, laterally spaced and aligned relation offset rearwardly from the divider flue element 40 are interposed in the downstream leg 42 extending the full height of the heat exchanger 25 and located in the zone immediately rearwardly of the exhaust outlet 33.

The flue elements 40 and 44 are all formed in an identical manner and each consists of two identical half shells or walls 45, 46, welded along their corresponding vertical edges into a single air conducting conduit and having corrugations 47 on opposite sides thereof arranged in a sinuous pattern, when viewed in horizontal cross section, extending the full height of the shell and located throughout the shells except for the immediate vertical edge portions thereof. The corrugations 47 in the half shells 45, 46, as well as the corrugations 39 in the sidewalls 26, 27, 28 and 31 of the heat exchanger, are inclined at a small angle to the direction of air flow. While the angle of the inclined corrugations may be varied, and depends largely on the width and length of the corrugations chosen for the half shells, the corrugations in one satisfactory example are /2 inch wide and 12 inches long, and are 2 or 3 degrees to the vertical edges of the half shells, and the half shells of each flue element are secured together in oppositely inclining relation so that corrugations of the confronting surfaces of each assembled set of shells comes in close proximity to each other at one or more points in the vertical distance through which the air passes between entering the bottom and leaving the top of the heat exchanger. As will be seen from the drawings, the corrugated half shells 45 and 46 collectively defining each flue element 44 are provided with mutually converging flanges 48 along their vertical edges while the uncorrugated top and bottom edges of the half shells extend slightly outwardly from the outmost reaches of the corrugations and are welded to the corresponding uncorrugated top and bottom edges of the opposite half shell of the next adjacent flue element to form a unitary array of flue elements. The uncorrugated top and bottom edges of the half shell 46 of the flue element 44 nearest the left hand vertical sidewall 26 are similarly welded to the uncorrugated top and bottom edges of the side wall 26 and the top and bottom edges of the half shell 45 of flue element 40 are welded to the top and bottom walls 29, 30 of the heat exchanger. In this manner, passages 49 are provided between the mutually confronting surfaces of each assembled pair of half shells 45, 46 which are open from bottom to the top of the heat exchanger and are in communication at the bottom of the heat exchanger with the space between the bottom wall 30 and the horizontal partition 20 to permit upward flow of air discharged from the blower 18 in the passages 49 between the half shells 45, 46 in intimate heat exchange relation with the heated products of combustion delivered from the burner 37 through the upstream leg 41, the connecting portion 43, and the downstream leg of the heat exchanger and conveyed through the tortuous gas passages 50 defined internally of the heat exchanger between the oppositely facing surfaces of the half shells of the adjacent flue elements 44.

The corrugated surfaces provided for the half shells 45, 46 and the heat exchanger exterior walls provide very large heat transfer surfaces per unit of projected area and permit thermal expansion with moderate stress. The inclined relationship of the corrugations and in relation to the direction of air flow causes impingement and scrubbing of the gases against the metal surfaces on opposite sides of the flow conduits, thereby substantially reducing the usual surface film thickness and correspondingly improving the rate of heat transfer. The crossing of flue forming surfaces on opposite sides of the gas and air conducting passages produces great turbulence without requiring direction changing bafiles and the like. With the corrugations inclined as illustrated in FIGURES 2 to 6, opposing corrugations cross each other, thus causing the heat absorbing air stream to be deflected from side to side in traveling through the air passages 49 from bottom to top of the heat exchanger and causing the heat dispensing gas stream likewise to be deflected as it travels from the combustion zone through the gas passages 50 to the exhaust outlet 33. This crisscross flue passage configuration has the unique characteristic of inherent difference in flow rate impedance between the two adjacent streams, the air stream flowing through passages 49 and the gas stream flowing through passages 50, so that each stream, while differing in volume, is maintained at a predetermined high velocity suitable to cause high heat flux through the enclosing walls.

While but one specific embodiment of the present invention has been particularly shown and described, it will be apparent that various modifications may be made therein within the spirit and scope of the invention, and it is desired, there-fore, that only such limitations be placed thereon as are imposed by the prior art and set forth in the appended claims.

What is claimed is:

1. In an air heater unit for supplying heated air to a space to be conditioned, a heat exchanger of generally box-like configuration having four enclosing side walls and two end walls joined together at their edges to form a leak-tight enclosure, said side walls generally paralleling a selected axis of the heat exchanger and being formed of corrugated sheet metal having corrugations defining ridges extending substantially uninterruptedly between said end walls along parallel corrugation axes inclined at a small angle to said selected axis, the corrugations of three of said side walls extending over substantially the whole area of their respective side walls, a fourth one of said side walls including said corrugations over substantially the whole area to one side of the center thereof and including means defining a single outlet port in said area and a single inlet port to the other side of the center thereof.

2. In an air heater unit for supplying heated air to a space to be conditioned, a heat exchanger of generally box-like configuration having four enclosing side walls and two end walls joined together at their edges to form a leak-tight enclosure, said side walls generally paralleling a selected axis of the heat exchanger and being formed of corrugated sheet metal having corrugations defining ridges extending substantially uninterruptedly between said end walls along parallel corrugation axes inclined at a small angle to said selected axis, the corrugations of three of said side walls extending over substantially the whole area of their respective side walls, a pair of joined sheet sections shaped to define a flue element therebetween, said sheet sections substantially paralleling each other and an opposite pair of said side walls and extending fully between said end walls at a location intermediate said opposite pair, said sheet sections being joined along one edge to a third one of said side walls and extending partially across the heat exchanger to divide the space within the latter into a substantially U-shaped space having first and second legs communicating with each other remote from said third side wall.

3. In an air heater unit, a heat exchanger as defined in claim 2, wherein each of said sheet sections is formed of corrugated sheet metal defining corrugation ridges over substantially the whole area thereof extending in parallelism to said corrugation axes, the axes of the corrugations of one of said sheet sections being inclined in opposite relation to the axes of the corrugations of the other said sheet sections and to the corrugation axes of the side Walls confronting the same.

4. In an air heater unit for supplying heated air to a space to be conditioned, a heat exchanger of generally box-like configuration having four enclosing side walls and two end walls joined together at their edges to form a leak-tight enclosure, said side walls generally paralleling a selected axis of the heat exchanger and being formed of corrugated sheet metal having corrugations defining ridges extending substantially uninterruptedly between said end walls along parallel corrugation axes inclined at a small angle to said selected axis, the corrugations of three of said side walls extending over substantially the whole area of their respective side walls, a plurality of flue elements within said heat exchanger spanning the distance between said end walls and located between a pair of said corrugated side walls substantially occupying the space to one side of the midplane between said pair, each of said flue elements being formed of a pair of like corrugated sheet sections joined along corresponding edges thereof paralleling said selected axis and having corrugations over substantially the whole area thereof extending between said end walls along inclined axes paralleling said corrugation axes, the inclined axes of the corrugations of the respective sheet sections being inclined in opposite directions, and the edges of said sheet sections 70 adjacent said end walls being joined together and to said end Walls with the spaces between the sheet sections of each flue element opening through said end walls for passage of air to be heated therethrough and the adjacent flue elements defining passages therebetween for flow of gaseous combustion products.

5. In an air heater unit, a heat exchanger as defined in claim 4, wherein the passage for flow of air between the sheet sections of each respective flue element is of larger cross section than the passages between respective flue sections for flow of gaseous combustion products.

6. In an air heating unit for supplying heated air to a space to be conditioned, a heat exchanger of generally box-like configuration having four enclosing side walls and two end walls joined together at their edges to form a leak-tight enclosure, said side walls generally paralleling a selected axis of the heat exchanger, a plurality of flue: elements within said heat exchangerspanning the distance between said end walls and located between a pair of said side walls substantially occupying the space to one side of the midplane between said pair, each of said flue elements being formed of a pair of like corrugated sheet sections joined along corresponding edges thereof paralleling said selected axis and having corrugations over substantially the whole area thereof defining ridges extending between said end walls along corrugation axes inclined at a small angle to said selected axis, the corrugation axes of the respective sheet sections being inclined in opposite directions, and the edges of said sheet sections adjacent said end walls being joined together and to said end walls with the spaces between the sheet sections of each flue element opening through said end walls for passage of air to be heated therethrough and the adjacent flue elements defining passages therebetween for flow of gaseous combustion products.

7. In an air heater unit, a heat exchanger as defined in claim 6, wherein the passage for flow of air between the sheet sections of each respective flue element is of larger cross section than the passages between respective flue sections for flow of gaseous combustion products.

8. In an air heater unit, a heat exchanger as defined in claim 6, including a pair of joined divider sheet sections shaped to define a divider flue element therebetween, said divider sheet sections substantially paralleling each other and an opposite pair of said side walls and extending fully between said end walls at a location intermediate said opposite pair, said divider sheet sections being joined along one edge to a third one of said side walls and extending partially across the heat exchanger to divide the space within the latter into a substantially U-shaped space having first and second legs communicating with each other remote from said third side wall, burner means communicating with said first leg adjacent said third side, means in said third side defining an outlet port communicating with said second leg for exhausting combustion products from the heat exchanger, and said plurality of flue elements being located in said second leg.

References Cited UNITED STATES PATENTS 1,780,984 11/1930 Shelton 126-116 2,194,733 3/1940 Andersen et al. 126-110 X 2,214,269 9/1940 Bryant 126-116 2,976,917 3/1961 Wyckofi et al 126-110 X FOREIGN PATENTS 848,095 9/ 1960 Great Britain.

CHARLES I. MYHRE, Primary Examiner US. Cl. X.R. 

